The present invention pertains to the art of making golf balls, and, more particularly, to a new die configuration for use in injection molding of golf ball layers and covers. The present invention relates to processes and apparatuses for forming multi-layer golf balls, and more particularly to processes and equipment for forming multi-layer golf balls having one or more deep dimples that extend through the outer cover layer to and/or into one or more layers or components thereunder.
Golf balls are typically made by molding a core of elastomeric or polymeric material into a spheroid shape. A cover is then molded around the core. Sometimes, before the cover is molded about the core, an intermediate layer is molded about the core and the cover is then molded around the intermediate layer. The molding processes used for the cover and the intermediate layer are similar and usually involve either compression molding or injection molding.
In compression molding, the golf ball core is inserted into a central area of a two piece die and pre-sized sections of cover material are placed in each half of the die, which then clamps shut. The application of heat and pressure molds the cover material about the core.
Blends of polymeric materials have been used for modem golf ball covers because certain grades and combinations have offered certain levels of hardness to resist damage when the ball is hit with a club and elasticity to allow responsiveness to the hit. Some of these materials facilitate processing by compression molding, yet disadvantages have arisen. These disadvantages include the presence of seams in the cover, which occur where the pre-sized sections of cover material were joined, and long process cycle times which are required to heat the cover material and complete the molding process.
Injection molding of golf ball covers arose as a processing technique to overcome some of the disadvantages of compression molding. The process involves inserting a golf ball core into a die, closing the die and forcing a heated, viscous polymeric material into the die. The material is then cooled and the golf ball is removed from the die. Injection molding is well-suited for thermoplastic materials, but has limited application to some thermosetting polymers. However, certain types of these thermosetting polymers often exhibit the hardness and elasticity desired for a golf ball cover. Some of the most promising thermosetting materials are reactive, requiring two or more components to be mixed and rapidly transferred into a die before a polymerization reaction is complete. As a result, traditional injection molding techniques do not provide proper processing when applied to these materials.
Reaction injection molding is a processing technique used specifically for certain reactive thermosetting plastics. As mentioned above, by xe2x80x9creactivexe2x80x9d it is meant that the polymer is formed from two or more components that react. Generally, the components, prior to reacting, exhibit relatively low viscosities. The low viscosities of the components allow the use of lower temperatures and pressures than those utilized in traditional injection molding. In reaction injection molding, the two or more components are combined and reacted to produce the final polymerized material. Mixing of these separate components is critical, a distinct difference from traditional injection molding.
The process of reaction injection molding a golf ball cover involves placing a golf ball core into a die, closing the die, injecting the reactive components into a mixing chamber where they combine, and transferring the combined material into the die. The mixing begins the polymerization reaction, which is typically completed upon cooling of the cover material.
The present invention provides a new mold or die configuration and a new method of processing for reaction injection molding a golf ball cover or inner layer which promotes increased mixing of constituent materials, resulting in enhanced properties and the ability to explore the use of materials new to the golf ball art.
For certain applications it is desirable to produce a golf ball having a very thin cover layer. However, due to equipment limitations, it is often very difficult to mold a thin cover. Accordingly, it would be beneficial to provide an apparatus and technique for producing a relatively thin cover layer.
Moreover, retractable pins have been utilized to hold, or center, the core or core and mantle and/or cover layer(s) in place within an injection mold while molding an outer cover layer thereon. In such processes, the core or mantled ball is supported in the mold using retractable pins extending from the inner surface of the mold to the outer surface of the core or mantled ball. The pins in essence support the core or mantled ball while the cover layer is injected into the mold. Subsequently, the pins are retracted as the cover material fills the void between the core or mantle and the inner surface of the mold.
However, notwithstanding, the benefits produced through the use of the retractable pins, the pins sometimes produce centering difficulties and cosmetic problems (i.e. pin flash, pin marks, etc.) during retraction, which in turn require additional handling to produce a golf ball suitable for use and sale. Additionally, the lower the viscosity of the mantle and/or cover materials, the greater the tendency for the retractable pins to stick due to material accumulation, making it necessary to shut down and clean the molds routinely. Accordingly, it would be desirable to provide an apparatus and method for forming a cover layer on a golf ball without the use of retractable pins.
The present invention provides, in a first aspect, an injection molding apparatus, preferably a reaction injection molding (xe2x80x9cRIMxe2x80x9d) apparatus for forming a golf ball defining a plurality of dimples along its outer surface and at least one deep dimple accessible from the outer surface. The molding apparatus comprises a first mold half defining a hemispherical first mold surface, and a second mold half defining a similar hemispherical second mold surface. The first and second mold surfaces have a plurality of raised regions that form dimples along the outer surface of the golf ball. The first and second mold surfaces also include provisions for receiving two or more flowable reactants used for forming the golf ball or a component thereof. The first and second mold surfaces include at least one outwardly extending protrusion that forms at least one deep dimple along the outer surface of the ball. The outwardly extending protrusion has a height greater than the height of any of the plurality of raised regions.
In a further aspect, the present invention provides a reaction injection molding apparatus for forming a golf ball core or intermediate ball assembly in which the molded component defines at least one deep dimple also along its outer surface. The molding apparatus comprises first and second mold halves that each define a hemispherical mold surface. Each of the hemispherical mold surfaces has (i) provisions for receiving two or more flowable reactants for forming the core or intermediate ball assembly, and (ii) at least one outwardly extending protrusion that forms a deep dimple along the outer surface of the core or intermediate ball assembly. The outwardly extending protrusion has a height that is greater than the thickness of the cover layer of the ball.
In another aspect, the present invention provides an injection molding apparatus adapted for forming a golf ball having an outer cover with at least one deep dimple defined along an outer surface of the golf ball. The molding apparatus comprises a first mold defining a generally flat first mating surface and a first concave hemispherical molding surface. The molding apparatus also comprises a second mold defining a generally flat second mating surface and a second concave hemispherical molding surface. The first and second molds are adapted to be placed in a molding configuration in which the first mating surface contacts the second mating surface, and the first molding surface and the second molding surface are aligned with each other to form a generally spherical molding chamber. The first and second molding surfaces include provisions for receiving flowable materials that form a molding material, and at least one protrusion having a height greater than the thickness of the cover layer of the golf ball.
A further aspect of the invention is to provide equipment and methods for forming a golf ball having a dimpled cover that is thinner than traditional cover layers.
Another aspect of the invention is to provide equipment and methods for forming a golf ball having dimples in an outer cover layer that extend to, and/or into, at least the next inner layer of the ball.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.